In the aftermath of the Dec. 14 massacre at a Connecticut elementary school, Mayors Against Illegal Guns earned the support of 13 more mayors, including several Republicans, raised tens of thousands of dollars, and lined up dozens of celebrities and technology executives to promote its cause.

Meanwhile, the Brady Campaign to Prevent Gun Violence and 32 families of mass shooting victims sent a letter to lawmakers and President Barack Obama demanding stricter gun laws.

Tragedies such as last week’s shooting provide a powerful emotional rallying point that gun control activists hope will finally tip the scales against better-funded, more politically influential gun rights groups. And the group best positioned to take advantage of any shift may be mayors, who can exert pressure on state legislatures and build support for their cause outside Washington, D.C.

In recent years, the Brady Campaign to Prevent Gun Violence has spent no more than $40,000 annually lobbying Congress and has had just one lobbyist on staff, while the National Rifle Association and other gun rights groups draw on hundreds of millions of dollars to pressure lawmakers on the Hill and at the ballot box.

The Brady Campaign — named for President Ronald Reagan’s press secretary, Jim Brady, who was permanently disabled in a 1981 assassination attempt — has for decades been the public face of gun control. But its footprint may soon be eclipsed by Mayors Against Illegal Guns, a nonprofit led by New York Mayor Michael Bloomberg.

The mayors’ group has only spent a touch more than the Brady Campaign — about $150,000 per year — but it is bolstered by Bloomberg’s high profile, billionaire war chest and new super PAC that spent $8.2 million targeting gun-friendly lawmakers in the 2012 election cycle.

In the three days following the shooting, the mayors’ group raised nearly $80,000 from small donors plus “some significant checks,” said Mark Glaze, a lobbyist at the Raben Group who represents the organization.

While the Brady Campaign has been focused on federal activity, Bloomberg and the mayors are taking their cause to state legislatures, with the support of a growing network of hundreds of local officials and law enforcement groups.

“We learned relatively quickly that [the NRA is] so used to being unopposed at the state level,” Glaze said. “That is one path to victory.”

He cited a recent victory in Michigan, where a coalition led by mayors helped defeat an NRA-backed bill that would have eliminated state-mandated background checks for all gun sales and dismantled a database that tracked transactions.

“Our team swung into action,” Glaze said. “We sent an organizer; we arranged a press conference, got the police together; we got our grass roots going ... and the NRA suffered this humiliating defeat.”

The bill, which easily passed the Michigan House of Representatives in June, died in the Senate after lawmakers voted for an alternate measure that retained the criminal background checks.

A separate bill passed the state legislature the day before the Sandy Hook Elementary School shooting that would allow gun owners to receive eight additional hours of training to carry their weapons in formerly gun-free areas. Michigan Republican Gov. Rick Snyder vetoed the bill Tuesday.

Bloomberg’s group does not focus on concealed-carry laws. Instead, it is fighting for background checks in all gun sales, including by private vendors, a new ban on assault weapons and high capacity magazines and stronger penalties for those who buy guns on behalf of those who don’t have clean records.

Among the group’s newest members are the mayors of Raleigh, N.C.; Tucson, Ariz.; Oak Creek, Wis.; and Maryville, Tenn., the birthplace of NRA-endorsed GOP Sen. Lamar Alexander.

Pamela Gilbert, a consumer advocacy lobbyist with Cuneo Gilbert & LaDuca LLP, said the groups would benefit from deeper coordination.

“Target and focus on the NRA as you would a corporate bad guy, not like another nonprofit or another policy group,” she said.